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Okay, so looked this up, and it looks like this is an idiomatic expression of sorts as it doesn't seem to strictly follow the typical usage of the も particle. Typically も does indicate "also" something.

Yet, something + もいいですか? seems to be the idiomatic way to say, "Can I do something"

Likewise, something + もいいです。 would be the way to say, "You can do something."

Correct me if I'm wrong to consider this somewhat of an idiomatic structure, and if there actually is a grammar rule that is being used here.